Large, four-wheel drive articulated tractors which utilize rear axle oscillation typically incorporate their rear axle with their rear frame so as to simultaneously oscillate the rear axle and rear frame relative to the front frame. Such simultaneous oscillation is usually provided through rather complex linkage systems which change the attitude of the vehicle and can, under some circumstances, adversely affect the life of the vehicle's drive line.
Another common means for oscillating the rear frame (and connected rear axle) involves the use of an A-frame with spherical ball bushings located above the rear axle's center line. The cost for such axle oscillation structure can be substantial.
Traditional axle oscillation necessitates the use of a support bearing on each axial side (front and rear) of the axle to be oscillated. When the oscillating axle is the rear axle, the support bearing arranged at the rear of such axle extends the vehicle behind the rear axle and thus causes loads drawn thereby to be pulled at a greater distance behind the rear tires or other ground engaging members. Such additional distance between the vehicle's rear tires and the load reduces the load necessary to raise the vehicle's front end or, in the alternative, causes additional weight to be added to the vehicle's front end.
U.S. Pat. No. 2,561,300 which issued July 17, 1951, illustrates a lift truck employing a cantilevered, oscillatable rear frame which is supported by dual support bearings arranged ahead of the rear axle. Such lift truck has no power transmitted to its rear wheels nor does it have a drawbar for pulling loads behind it. Since the entire rear frame of the subject lift truck oscillates, expense for building the same may be substantially greater than if the axle alone oscillated. U.S. Pat. No. 1,540,413 which issued June 2, 1925, illustrates a draw bar which is biased forward by a spring and is fixably attached to the tractor rear axle and the tractor frame. Since the illustrated tractor's frame and rear axle are attached, oscillation of the rear axle is restricted as is oscillation of the drawbar which is fixed thereto.